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Length extension attack - Wikipedia

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In cryptography and computer security, a length extension attack is a type of attack where an attacker can use Hash(message1) and the length of message1 to calculate Hash(message1 ‖ message2) for an attacker-controlled message2, without needing to know the content of message1. This is problematic when the hash is used as a message authentication code with construction Hash(secret ‖ message),[1] and message and the length of secret is known, because an attacker can include extra information at the end of the message and produce a valid hash without knowing the secret. Algorithms like MD5, SHA-1 and most of SHA-2 that are based on the Merkle–Damgård construction are susceptible to this kind of attack.[1][2][3] Truncated versions of SHA-2, including SHA-384 and SHA-512/256 are not susceptible,[4] nor is the SHA-3 algorithm.[5] HMAC also uses a different construction and so is not vulnerable to length extension attacks.[6] A secret suffix MAC, which is calculated as Hash(message ‖ secret),

Length extension attack - Wikipedia Jump to content From Wikipedia, the free encyclopedia Attack against cryptographical hash functions In cryptography and computer security , a length extension attack is a type of attack where an attacker can use Hash ( message 1 ) and the length of message 1 to calculate Hash ( message 1 ‖ message 2 ) for an attacker-controlled message 2 , without needing to know the content of message 1 . This is problematic when the hash is used as a message authentication code with construction Hash ( secret ‖ message ), [ 1 ] and message and the length of secret

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